The present invention is directed to braking devices for bicycles and, more particularly, to a brake device which is supported by fastening pins extending from seats installed on the front fork or rear fork of a bicycle, and which is driven by a brake wire so that brake shoes are pressed against the rim of the corresponding wheel.
In the case of bicycles which allow off-road riding (known as mountain bikes (MTB) or all-terrain bikes (ATB)), cantilever type brake mechanisms are generally mounted on the bicycles in order to provide a strong braking force. One end of each of the brake arms is supported on the front fork or rear fork so that the end is free to pivot, while the other end of each brake arm is connected to the brake wire. The brake shoes are installed on intermediate portions of the brake arms so that the brake shoes face both side surfaces of the bicycle wheel rim.
In such a cantilever type bicycle brake mechanism, the brake arms are caused to pivot in the closing direction by using a brake lever to pull the brake wire. As a result, the brake shoes are pressed against the aforementioned rim so that braking is applied. Such a cantilever type brake mechanism offers many advantages. For example, there is no need to alter the shape of the brake mechanism in accordance with the size of the bicycle (as is necessary in the case of caliper brake mechanisms). Furthermore, braking force tends to be much more even than with caliper brake mechanisms.
Unfortunately, cantilever type brake mechanisms suffer from problems of their own. For example, if the brake shoes pivot downward from the horizontal plane as a result of the pivoting of the brake arms, so that the brake shoes contact the side surfaces of the rim without conforming to the inclination of the side surfaces, then the pressing force of the brake shoes is reduced. Accordingly, it is necessary to adjust the relative attachment positions of the rim side surfaces and the brake mechanism with a high degree of precision, and such adjustment work is difficult.
One technique for solving this problem is disclosed in Japanese Patent Application Kokoku No. 62-1873. The brake mechanism disclosed in this document is constructed from [a] brake arms which are supported on fastening pins (extending from seats) so that the brake arms are free to pivot, with the upper ends of the brake arms being positioned to the outside of the fastening pins, [b] output links which are supported at intermediate points on the brake arms so that the output links are free to pivot, and which extend outward, [c] driven links which are connected to the aforementioned output links so that the driven links are free to pivot, and which extend downward, and [c] stationary links which are connected to the aforementioned driven links in a manner that allows free pivoting, and which also extend inward and are fastened to the aforementioned fastening pins in a manner that prevents pivoting. In this brake mechanism, the brake arms are caused to pivot upward by the brake wire, thus causing the driven links to pivot inward, so that the output links move in a horizontal or upward-facing attitude. As a result, the brake shoes contact the sides surfaces of the rim in a horizontal or upward-facing attitude.
Unfortunately, with this structure, the driven links are positioned outside the brake arms, so that the width dimension of the brake mechanism is increased. As a result, in cases where this brake mechanism is used as a front brake, the front brake tends to strike the rider's shins, etc., when the handlebars are turned. Furthermore, in cases where the brake mechanism is used as a rear brake, the brake mechanism tends to strike the rider's heels or calves, etc., while the rider is pedaling.